The kinetics and mechanism of the thermal decomposition of CH 3 SO 2 and its reaction with NO 2 have been investigated in a discharge flow reactor at 298 K and 1 Torr pressure using Cl/Cl 2 /CH 3 SH/NO 2 /He mixtures:. The rate constants k 3 and k 4 were derived from the fitting of calculated and experimental kinetic profiles of CH 3 O and SO 2 monitored by laser-induced fluorescence (LIF) analysis. CH 3 produced in reaction 4 was rapidly converted into CH 3 O by reaction with NO 2 . The values obtained were k 3 ) (2.2 ( 1.1) × 10 -12 cm 3 molecule -1 s -1 and k 4 ) 510 ( 150 s -1 . Errors are 1 standard deviation. The role of these reactions in the atmospheric oxidation mechanism of dimethyl sulfide is discussed.

The kinetics of CzH50 and CzH502 radicals with NO have been studied at 298 K using the discharge flow technique coupled to laser induced fluorescence (LIF) and mass spectrometry analysis. The temporal profiles of CzH5O were monitored by LIF. The rate constant for CzH5O + NO -Products (21, measured in the presence of helium, has been found to be pressure dependent: hz = (1.25 2 0.04) X (1.66 2 0.06) x 10-11, (1.81 t 0.06) X 10-l' a t P (He) = 0.55, 1 and 2 torr, respectively (units are cm3 molecule-l s-I). The Lindemann-Hinshelwood analysis of these rate constant data and previous high pressure measurements indicates competition between association and disproportionation channels: CzH50 + NOThe following calculated average values were obtained for the low and high pressure limits of kza and for k2b : kga = (2.6 ? 1.0) X cm6 molecule-' s-I, kra = (3.1 ? 0.8) X cm3 molecule-' s-' and kzb ca. 8 X lo-'' cm3 molecule-' s-l. The present value of hga, obtained with He as the third body, is significantly lower than the value (2.0 % 1.0) x 10-27 cm6 molecule-2 s-l recommended in air. The rate constant for the reaction CzH502 + NO + C2H50 + NO2 (3) has been measured at 1 torr of He from the simulation of experimental CzH5O profiles. The value obtained for h3 = (8.2 2 1.6) X cm3 molecule-' s-' is in good agreement with previous studies using complementary methods.

A discharge flow reactor coupled to laser-induced fluorescence and mass spectrometry, for the detection of ethoxy and nitrate radicals, respectively, has been used to study the kinetics of the reactions of C 2 H 5 O and C 2 H 5 O 2 with NO 3 at ca. 1 Torr of helium and 298 K. From the analysis of the C 2 H 5 O concentration-time profiles in two sets of experiments, the reactions C 2 H 5 O + NO 3 f C 2 H 5 O 2 + NO 2 (1) and C 2 H 5 O 2 + NO 3 f C 2 H 5 O + NO 2 + O 2 (2) were observed to be strongly coupled. The rate constants were derived from modeling calculations, k 1 ) (3.3 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 and k 2 ) (2.3 ( 0.5) × 10 -12 cm 3 molecule -1 s -1 . These data are compared with other very recent literature data, and their atmospheric significance for nighttime chemistry is briefly discussed.HNO 3 was flowed out by helium carrier gas from a bubbler containing a liquid mixture H 2 SO 4 /HNO 3 (2:1) maintained at T X